Berkley, Intrinsic Pulmonary Nerves. 109 



final terminations are simple bulbs. All the end-knobs are ap- 

 parently situated between the muscular fibres without especial 

 relation to their nuclei, so far as we have been able to determ- 

 ine. [2]. Numbers of fibres, branched and unbranched, pass 

 through and beyond the muscular zone, and form a sub-epithe- 

 lial plexus, in the mucous layer. This plexus is quite distinct 

 and well developed, not only in the larger bronchi, but also 

 in divisions of the second and third order ; and forms a circular 

 network of interlacing and connecting filaments around the bases 

 of the epithelial infoldings. From this meshwork nerve fibres 

 ascend upon the fibrous tissue in the centre of the epithelial 

 folds, some nearly to the apices, others only half way, and there 

 terminate in knob-form [Fig. 2]. No trace of any ending is 

 to be seen entering the cement substance between the columnar 

 epithelial cells. 



On the smallest bronchi, when the surrounding muscular 

 cells have become very greatly diminished in numbers, the 

 nerve arrangement is somewhat different, there is now only one 

 plexus or network, and from its fibres new twigs penetrate 

 quite numerously into the epithelial layer, where they terminate 

 in end-knobs, after the development of curious arborescent 

 figures with many thickenings and nodosities [Fig. 3]. These 

 end terminations seem distinctly to lie between the outermost 

 margins of the flattened epithelial cells surrounding the lumen 

 of the tube, quite close to the fibrous layer. 



In all the fibres of the networks, both peri-bronchial and 

 mucous, are developed local thickenings and varicosities, but 

 true ganglionic cells within the muscular layer have not been 

 seen. That the ganglionic developments found in the paths 

 of the fibres coming from the terminal arborizations in the 

 epithelium of the bronchioles act the part of intermediate trans- 

 mitters of nerve impressions from the epithelial surface of the 

 air tubes, as is the case with some of the organs of special 

 sense, in particular the cutaneous surfaces [see the studies of 

 Retzius^ and Lenhossek^ on Lumbricus] to nerve cells in more 



^Biol. Untersuch. Neue Folge IV, 1892, Stockholm. 

 ^Arch. f. Mik. Anat. Bd. 39, 1892. 



